Toughened Resin Fiber Laminates with Titanium Particles

ABSTRACT

A composite structure includes at least one resin matrix layer having a resin material and a plurality of fiber elements and a plurality of titanium particles provided in the resin material. A method of toughening a resin matrix layer is also disclosed.

TECHNICAL FIELD

The disclosure relates to polymer composite structures. Moreparticularly, the disclosure relates to a polymer composite structurehaving a resin matrix interlayer interfused with titanium particles to“toughen” resin fiber laminates and increase the compression loadcapacity after sustaining impact damage.

BACKGROUND

Polymer composite materials selected and qualified for variousapplications, such as with primary structure applications in themanufacture of aircraft, for example and without limitation, may beevaluated for two key mechanical properties: compression-after-impact(CAI) strength and hot-wet compression strength, and more specificallyopen-hole-compression (OHC) strength. However, the means for increasinga composite material's CAI strength and hot-wet OHC strength havetypically been counterproductive to each other. More specifically,traditional particulate interlayer toughening methods using elastomericor thermoplastic-based polymer particles have been effective forincreasing a composite's CAI strength, but not generally effective forsimultaneously increasing hot-wet compression strength (e.g., hot-wetOHC) properties and, more typically, result in a tradeoff relationshipwith one another.

Conventional methods utilized to increase the hot-wet compressionstrength properties of a polymer composite may involve increasing theresin matrix crosslink density to increase the elastic modulus of theresin or by reducing the water absorption characteristics of the matrixby proper formulation of the resin's specific chemistry. Effortsassociated with increasing the matrix crosslink density to increasehot-wet compression strength typically result in a composite havingreduced CAI properties.

In the interest of toughening the composite matrix interlayersufficiently to improve its CAI strength, it will be appreciated thattitanium particles are irregularly-shaped (small pieces of Ti sponge)and should provide a mechanical bond within the epoxy, along with theductility and function of a “blocker” for crack propagation. In view ofthe foregoing, it would be highly desirable to provide a polymercomposite structure having a matrix interlayer which provides theproperties of titanium but which does not significantly add to theweight of the overall structure, and also which does not negativelyaffect the hot-wet compression strength of the matrix interlayer.

SUMMARY

The disclosure is generally directed to a composite structure. Anillustrative embodiment of the composite structure includes at least oneresin matrix layer having a resin material and a plurality of fiberelements and a plurality of titanium particles provided in the resinmaterial.

The disclosure is further generally directed to a method of toughening aresin matrix layer. An illustrative embodiment of the method includesproviding a resin matrix layer having a resin material, providing aplurality of fiber elements in the resin material of the resin matrixlayer and providing a plurality of titanium particles in the resinmaterial of the resin matrix layer.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

FIG. 1 is a cross-sectional view of a polymer composite structure havinga pair of resin matrix interlayers interfused with titanium particles.

FIG. 2 is a flow diagram which illustrates an illustrative method oftoughening a resin matrix interlayer.

FIG. 3 is a flow diagram of an aircraft production and servicemethodology.

FIG. 4 is a block diagram of an aircraft.

DETAILED DESCRIPTION

Referring to FIG. 1, an illustrative embodiment of a composite structure1 is shown. The composite structure 1 may include a first fiber layer 2,a second fiber layer 3 and a third fiber layer 4 each of which mayinclude multiple fiber elements or filaments 5. The fiber elements orfilaments 5 may be carbon fiber prepreg, for example and withoutlimitation, and may be oriented in generally parallel relationship withrespect to each other. The carbon fiber prepreg may be manufactured withcarbon filaments that are highly collimated unidirectionally in a tapeform and held to tight dimensional tolerances in thickness across thewidth and length of the composite structure 1. Prior to cure, carbonfibers which are impregnated with resin may be limp and drapable,allowing the tape to conform to part molds.

A first resin matrix interlayer 8 may be interposed between the firstfiber layer 2 and the second fiber layer 3. A second resin matrixinterlayer 10 may be interposed between the second fiber layer 3 and thethird fiber layer 4. The first resin matrix interlayer 8 may bond thefirst fiber layer 2 to the second fiber layer 3 and the second resinmatrix interlayer 10 may bond the second fiber layer 3 to the thirdfiber layer 4 to form a single, unitary composite structure 1.

Each of the first resin matrix interlayer 8 and the second resin matrixinterlayer 10 may include a resin material 14 such as epoxy, for exampleand without limitation. Multiple fiber elements or filaments 9 mayextend through the resin material 14. The fiber elements or filaments 9may be carbon fiber prepreg, for example and without limitation, and maybe oriented in generally parallel relationship with respect to eachother and in generally 90-degree relationship with respect to the fiberelements or filaments 5 in each of the first fiber layer 2, the secondfiber layer 3 and the third fiber layer 4. It will be appreciated thatthe particular arrangement of the fiber elements or filaments 5 in eachof the first fiber layer 2, the second fiber layer 3 and the third fiberlayer 4 and of the fiber elements or filaments 9 in each of the firstresin matrix interlayer 8 and the second resin matrix interlayer 10 maybe varied according to the requirements of a particular application andthat the arrangement of the fiber elements or filaments 5 and the fiberelements or filaments 9 at a 90 degree angle is only for illustrativepurposes.

Titanium particles 12 may be intermixed in the resin material 14 of eachof the first resin matrix interlayer 8 and the second resin matrixinterlayer 10. The titanium particles 12 may be graded titanium spongeparticles, for example and without limitation. The titanium particles 12may be dispersed generally uniformly throughout the resin material 14and may be present in the resin material 14 in a quantity of from about0.3% to about 30% by volume. In some illustrative embodiments, each ofthe titanium particles 12 may have a diameter of from about 1 to about90 microns. In some applications, sizes of the titanium particles 12 ofabout 3˜6 microns for unidirectional tape and about 7˜10 microns forwoven fabric may be beneficial. The titanium particles 12 may be 99˜100%commercially-pure Ti sponge derived from the Kroll extraction processand may be graded/screened for size.

The titanium particles 12 may increase the CAI strength of the firstresin matrix interlayer 8 and the second resin matrix interlayer 10,serving to toughen the interlayers 8, 10 against microcracking anddelamination but without the negative impact of lowering the hot-wetcompression strength of the overall polymer composite structure 1. Thismay be due in part to the fact that the use of the titanium particles 12may eliminate the need to use elastomeric particles or thermoplasticparticles, which may more typically be used to strengthen the compositelaminate interlayer but which are known to absorb water in the resin,and therefore result in a reduction in the hot-wet compression strengthof the interlayers 8, 10. The titanium particles 12 may not absorbwater, and therefore may not negatively impact the hot-wet compressionstrength of the interlayers 8, 10. The presence of the titaniumparticles 12 in the interlayers 8, 10 may allow the use of cheaper resinsystems by improving the properties of the resin. Due to improvement inthe impact resistance of the composite structure 1, fewer plies ofcarbon-epoxy laminates may be required.

It will also be appreciated that use of the titanium particles 12 as aresin additive may provide the added benefit of serving to disperse theenergy of an electric charge, such as from a lightening strike, moreevenly throughout the composite structure 1. This may be important inaerospace applications in which the composite structure 1 may be used toform a portion of an aircraft that could experience lightening strikeduring operation. The titanium particles 12 may effectively serve tospread out or dissipate the electric charge over a greater area of thecomposite structure 1, thereby reducing the likelihood of damage to alocalized portion of the composite structure 1.

Still another advantage of the titanium particles is that they may nottangibly increase the overall weight of the composite structure 1 due tothe resultant gains in overall strength of the composite structure 1under hot/wet conditions which may limit the performance envelope forpolymer composite structures. Designs may be possible with fewer pliesof prepeg (carbon fiber-epoxy) and still meet certain damage impactrequirements. This may be particularly important in aerospaceapplications in which lightweight, yet structurally-strong componentsare highly important. Moreover, the use of titanium sponge particles inthe matrix interlayer may not require significant modification toexisting composite part fabrication processes where composite structuresare formed using preimpregnated (prepreg) materials and are easilyincorporated into advanced composite part fabrication processes notinvolving prepeg material forms [e.g. resin transfer molding (RTM),vacuum assisted resin transfer molded (VARTM), resin infusion, etc.].

The use of titanium particles 12 may be anticipated to providesignificant resistance to impact damage of the composite structure 1.This is because titanium may be capable of absorbing a significantdegree of impact and deformation due to its elongation properties. Thismay be anticipated to provide a significant load-velocity impactresistance. Titanium may also have significant vibration dampeningproperties that may help to improve the fatigue life of the compositestructure, which may be an especially desirable characteristic foraircraft and spacecraft structures. The titanium particles may be ableto dampen impact energies (i.e. shock) to protect against delaminationof the independent plies of the composite structure and act as avibration/shock energy absorber (i.e. sink) to help significantlydissipate impact energies experienced by the composite structure.

It will be appreciated that the quantity of titanium particles 12 byvolume in the resin material 14 can vary significantly to suit the needsof a specific application. The resin matrix interlayer 8, 10 maycomprise about 0.3%-30% particles by volume, but these particles may beutilized in significantly higher concentrations as a discontinuous,particle-rich layer approaching the morphology similar to a discrete,continuous metal ply as in fiber-metal laminates. Alternatively, alesser concentration of the particles may be used to suit a specificapplication.

The use of titanium particles 12 may be predicted to provide a number ofadditional advantages such as good corrosion and wear (i.e, erosion)resistance relative to the base laminate. When it is added to athermosetting polymer composite, titanium may improve the G_(1c)/G_(11c)properties (i.e., mechanical properties reflecting fracture resistance)of the composite. The titanium particles 12 may also providesignificantly improved electrical conductivity for the compositestructure 1 to thus improve its durability relative to repeatedlightning strikes. The overall durability of the outer surface of thecomposite structure 1 may also be improved (i.e. regarding wear anderosion resistance).

Titanium sponge powder may have little impact on current manufacturingprocesses. More specifically, titanium sponge powder may not requiresignificant modification to ATLM (Automated Tape Laying Machining),hot-drape forming, advanced fiber placement (AFP) and hand lay-upoperations. The use of titanium sponge particles may also be readilyapplicable to Resin Transfer Molding (RTM), Vacuum Assisted ResinTransfer Molding (VARTM) and Seamann Composite's Resin Injection MoldingProcess (SCRIMP), where the titanium particles are added to the surfaceof the preform's fibers or partitioned between layers of the preform'splies prior to the resin impregnation process. Still another uniquebenefit to the use of particle-toughened composite structure may includeits ability to be utilized in a form equivalent to prepeg materialscurrently used (i.e., unidirectional tape and fabric prepegs) withoutimpacting current machine processes. The particle-toughened compositecould possibly also act as a “drop-in” replacement for current materialsused in such processes as Automated Tape Laying Machining (ATLM),advanced fiber placement (AFP), hot-drape forming and conventional handlayup. As will be appreciated, the use of titanium sponge particleswithin the interlayers of a composite structure may have significantspecific advantages to aircraft structures. The vibration dampeningcharacteristics of the titanium particles may significantly enhance thefatigue-life of aircraft structures. In space applications, in whichstiff composite structures may be subjected to extreme acoustic andstructural vibrations during launch, the particles may provide addedprotection against delamination and fracturing of the interlayers.

The utilization of titanium sponge particles as a resin matrix additivemay provide the benefit of toughening the composite laminate, as well asproviding additional performance benefits to the structure as was notedherein above. This metallic powder may provide benefits of upgradingstrength qualities in existing lower cost epoxy systems, i.e. the 250 Fcure systems, along with 350 F neat resin systems. There may be otherpossible beneficial uses such as, but not limited to, flame retardants;electronic heat sinks; ballistic protection; providing soundabsorbing/barrier qualities; and raising the properties of hightemperature epoxies, bismaleimide (BMI) and polymerization of monomericreactants (PMR) polyimide monomers. The toughening system may not belimited to laminates with graphite/carbon fibers, as glass, aramid, andboron fibers, along with the possible use with thermoplastics [e.g.high-density polyethylene (HDPE), ultra high molecular weightpolyethylene (UHMWPE), polyetheretherketone (PEEK),polyetherketoneketone (PEKK), etc.] may also be beneficial andfunctional. The particle additive may enable the practical use oftitanium in composite materials and may further enable the compositematerial to serve as a “drop-in” material for current and advancedproduction processes in the manufacture of composite parts of variousdesign complexities.

Referring next to FIG. 2, a flow diagram which illustrates anillustrative method of toughening a resin matrix layer is shown. Inblock 202, a resin matrix layer having a resin material is provided. Theresin material of the resin matrix layer may be epoxy, for example andwithout limitation. In block 204, fiber elements or filaments areprovided in the resin material of the resin matrix layer. The fiberelements or filaments may be carbon fiber prepreg, for example andwithout limitation, and may be highly collimated unidirectionally in atape form. In block 206, titanium particles are provided in the resinmaterial of the resin matrix layer. The titanium particles may have adiameter of from about 1 to about 90 microns and may be present in theresin matrix layer in a quantity of about 0.3% to about 30% by volume.The titanium particles may be graded titanium sponge particles, forexample and without limitation. In some applications, thetitanium-strengthened resin matrix layer may be a resin matrixinterlayer which bonds a first fiber layer to a second fiber layer in apolymer composite structure.

Referring next to FIGS. 3 and 4, embodiments of the disclosure may beused in the context of an aircraft manufacturing and service method 78as shown in FIG. 3 and an aircraft 94 as shown in FIG. 4. Duringpre-production, exemplary method 78 may include specification and design80 of the aircraft 94 and material procurement 82. During production,component and subassembly manufacturing 84 and system integration 86 ofthe aircraft 94 takes place. Thereafter, the aircraft 94 may go throughcertification and delivery 88 in order to be placed in service 90. Whilein service by a customer, the aircraft 94 may be scheduled for routinemaintenance and service 92 (which may also include modification,reconfiguration, refurbishment, and so on).

Each of the processes of method 78 may be performed or carried out by asystem integrator, a third party, and/or an operator (e.g., a customer).For the purposes of this description, a system integrator may includewithout limitation any number of aircraft manufacturers and major-systemsubcontractors; a third party may include without limitation any numberof vendors, subcontractors, and suppliers; and an operator may be anairline, leasing company, military entity, service organization, and soon.

As shown in FIG. 4, the aircraft 94 produced by exemplary method 78 mayinclude an airframe 98 with a plurality of systems 96 and an interior100. Examples of high-level systems 96 include one or more of apropulsion system 102, an electrical system 104, a hydraulic system 106,and an environmental system 108. Any number of other systems may beincluded. Although an aerospace example is shown, the principles of theinvention may be applied to other industries, such as the automotiveindustry.

The apparatus embodied herein may be employed during any one or more ofthe stages of the production and service method 78. For example,components or subassemblies corresponding to production process 84 maybe fabricated or manufactured in a manner similar to components orsubassemblies produced while the aircraft 94 is in service. Also, one ormore apparatus embodiments may be utilized during the production stages84 and 86, for example, by substantially expediting assembly of orreducing the cost of an aircraft 94. Similarly, one or more apparatusembodiments may be utilized while the aircraft 94 is in service, forexample and without limitation, to maintenance and service 92.

Although the embodiments of this disclosure have been described withrespect to certain exemplary embodiments, it is to be understood thatthe specific embodiments are for purposes of illustration and notlimitation, as other variations will occur to those of skill in the art.

1. A composite structure, comprising: at least one resin matrix layerhaving a resin material and a plurality of fiber elements and aplurality of titanium particles provided in said resin material.
 2. Thecomposite structure of claim 1 wherein said resin material comprisesepoxy.
 3. The composite structure of claim 1 wherein said plurality offiber elements comprises carbon fiber prepreg.
 4. The compositestructure of claim 1 wherein said plurality of titanium particlescomprises a plurality of graded titanium sponge particles.
 5. Thecomposite structure of claim 1 wherein said plurality of titaniumparticles is present in said at least one resin matrix layer in aquantity of from about 0.3% to about 30% by volume.
 6. The compositestructure of claim 1 wherein each of said plurality of titaniumparticles has a diameter of from about 1 micron to about 90 microns. 7.The composite structure of claim 1 wherein said plurality of titaniumparticles is uniformly dispersed throughout said resin material.
 8. Acomposite structure, comprising: a first fiber layer having a first setof fiber elements; a second fiber layer having a second layer of fiberelements; a resin matrix interlayer having a resin material interposedbetween said first fiber layer and said second fiber layer; a pluralityof fiber elements provided in said resin material of said resin matrixinterlayer; and a plurality of titanium particles provided in said resinmaterial of said resin matrix interlayer.
 9. The composite structure ofclaim 8 wherein said resin material comprises epoxy.
 10. The compositestructure of claim 8 wherein said plurality of fiber elements comprisescarbon fiber prepreg.
 11. The composite structure of claim 8 whereinsaid plurality of titanium particles comprises a plurality of gradedtitanium sponge particles.
 12. The composite structure of claim 8wherein said plurality of titanium particles is present in said at leastone resin matrix layer in a quantity of from about 0.3% to about 30% byvolume.
 13. The composite structure of claim 8 wherein each of saidplurality of titanium particles has a diameter of from about 1 micron toabout 90 microns.
 14. The composite structure of claim 8 wherein saidplurality of titanium particles is uniformly dispersed throughout saidresin material.
 15. The composite structure of claim 8 wherein saidplurality of fiber elements of said resin matrix interlayer is orientedin generally perpendicular relationship with respect to said first setof fiber elements of said first fiber layer and said second set of fiberelements of said second fiber layer. 16-20. (canceled)